Hypothalamus

Amylin Receptor

Amylin is released alongside insulin and signals fullness through a different brain pathway than GLP-1. That is the whole argument for cagrilintide: two satiety routes at once rather than a bigger dose of one.

GIP Receptor

The second incretin receptor. Adding it to GLP-1 agonism is what separates tirzepatide from semaglutide: more energy expenditure and a direct effect on fat tissue, on top of the appetite drop.

GLP-1 Receptor

The incretin receptor behind semaglutide and every drug in that class. Three separate effects run through it: appetite suppression in the brain, slower stomach emptying, and glucose-dependent insulin release from the pancreas.

Ghrelin Receptor

What ghrelin binds to make the pituitary release growth hormone, and what every GHRP and MK-677 is built to hit. It also carries the hunger signal, which is why some GH secretagogues make you ravenous and others do not.

Kisspeptin Receptor

One step above GnRH. Kisspeptin neurons are the master switch that tells the hypothalamus to release GnRH at all, which is why acting here produces a physiologic LH pulse rather than overriding the axis.

Melanocortin 3 Receptor

A central melanocortin receptor involved in energy balance and sexual arousal. It is one of the two receptors PT-141 works through.

Melanocortin 4 Receptor

The melanocortin receptor that controls appetite and central sexual arousal. It is why the melanotans suppress hunger and cause spontaneous erections, and why PT-141 works in the brain rather than in the blood vessels the way a PDE5 inhibitor does.

HPA Axis Activity

The stress axis: hypothalamus to pituitary to adrenal cortex, ending in cortisol. Relevant to mood twice over. A compound that blocks the glucocorticoid receptor removes the brake the axis runs on, and a compound that shuts down the gonadal axis leaves this one carrying more of the load.

Sleep Quality

How restorative sleep is, as opposed to how much of it there is. Deep and REM sleep are where growth hormone is released and where memory is consolidated, so this is the measure that connects a sleep effect to a memory effect. A person can sleep eight hours and get almost none of this.